In a case where AD conversion is performed in a limited area, for example, in a pixel, a system having most favorable area efficiency, in signal reading systems for a solid-state image pickup device, is an integrating-typed (slope-typed) AD conversion system including a comparator and a digital circuit at the subsequent stage of the comparator.
Non-Patent Document 1 has proposed a technology of achieving AD conversion in a limited area with the integrating-typed AD conversion system. For example, the system of Non-Patent Document 1 has a circuit configuration of inputting a slope signal into a comparator a plurality of times with one DRAM circuit being a digital circuit at a subsequent stage. For example, the same slope signal is repeatedly input into the comparator eight times for 8-bit AD conversion. Then, an operation of storing, into the DRAM circuit, a code of 0 or 1 at a point in time in which the output of the comparator is inverted, is repeated eight times so that the storage is read to the outside at a point in time in which comparison over the entire surface is completed.